English
If f is surjective, then the n-th derived subgroup of G' is contained in the image of the n-th derived subgroup of G: derivedSeries(G',n) ≤ (derivedSeries(G,n)).map f.
Русский
Если f сюръективен, то n-й член производящей серии G' включён в образ n-й члены производящей серии G: derivedSeries(G',n) ≤ (derivedSeries(G,n)).map f.
LaTeX
$$derivedSeries(G',n) ≤ (derivedSeries(G,n)).map f$$
Lean4
theorem derivedSeries_le_map_derivedSeries (hf : Function.Surjective f) (n : ℕ) :
derivedSeries G' n ≤ (derivedSeries G n).map f := by
induction n with
| zero => exact (map_top_of_surjective f hf).ge
| succ n ih => exact commutator_le_map_commutator ih ih